In flexible exhaust couplings used behind a diesel engine (on-highway and off-highway) there are observed high failure rates of the couplings. The nature of the diesel engine creates a very severe NVH (noise, vibration, harshness) environment which is detrimental to adjacent components and more specifically the flexible coupling in the exhaust system. Such systems typically have a low spring stiffness bellow having a low natural frequency that easily aligns with the vibration profile of the application's diesel engine. That leads to accelerated fatigue and abrasion failure. In addition, increasing government-mandated emission requirements mandate the use of ATD's (after treatment devices) in diesel exhaust systems. Such ATDs typically include at least two functional components, a diesel particulate filter (DPF) and a Selective Catalytic Reduction (SCR). With regard to the DPF, elevated exhaust temperatures are required to periodically clean it. Gas temperature loss in any system flexible coupling renders this process less efficient. Thus undesirable temperature losses in the prior couplings reduce the system's efficiency in cleaning periodically. Respecting the SCR, the chemical conversion of undesirable NOx to non-harmful chemicals like N2, H2O and CO2 requires high temperatures such as in the range of 357° C. and 447° C. Exhaust gas temperature loss in prior flexible couplings renders the conversion less efficient. Thus it is desired to reduce loss of exhaust gas temperatures across flexible couplings used in such exhaust systems and to increase the efficiency of the ATD systems in order to meet federal emission standards.
Others have interposed materials between a bellow and a liner to reduce thermal loss and wear in the coupling. Nevertheless, such prior efforts as are known are limited to static spacers which cannot move dynamically, or which are positively connected to the bellow, or of static length, thereby of limited dynamic effect as the bellows and liner move from one configuration to another due to thermal, dynamic or assembly stresses in the coupling.
Such prior efforts, for example are described in U.S. Patent Publication No. US 2011/0074147; U.S. Pat. No. 8,453,680; German Patent document DE 10 2011 110 147 A1; and German Patent document DE 20 2006 008 811 U1, incorporated herein as background. See also FIG. 7 illustrating prior structures wherein liner movement allows direct, undesirable contact.
It is thus one objective of this invention to provide an improved coupling with reduced failure rates, reduced NVH and reduced thermal heat loss from liner to bellow, with increased thermal heat retention inside the coupling.
A further objective of the invention has been to provide a coupling of liner and bellow configuration with a dynamic feature providing beneficial function to a degree not shown or suggested in known prior art.